LOUDON, N.H. (AP) — New Hampshire's forest rangers are cautioning visitors to this weekend's NASCAR race: If you're camping, buy the firewood locally or have a certificate showing it's been heat-treated.

They're trying to slow the spread of the emerald ash borer, an invasive species that has destroyed millions of ash trees over the past decade. It's been found in some areas of New Hampshire.

Rangers will inspect firewood coming into New Hampshire Motor Speedway from July 9-11. The campground at the speedway is the largest in the state and the race attracts more than 100,000 fans.

Firewood that doesn't meet the requirements will be confiscated and immediately burned under New Hampshire's out-of-state quarantine. Repeat violators will be ticketed.

The inspections are publicized on the speedway's website and notices were sent with mailed tickets.